1. Field of the Invention
This invention generally relates to a multimedia data processing apparatus with reduced buffer size, and more particularly, to a multimedia data processing apparatus with reduced buffer size for direct memory access in an image system.
2. Description of the Related Art
Referring to FIG. 1, in a conventional image system, a multimedia data processing apparatus 10 includes an accessing unit 11 and a processing unit 12. The accessing unit 11, which can be implemented by a direct memory access (DMA), has a plurality of buffers 111, 112, . . . to 11n therein, which are coupled to a share-bus system 90 through a plurality of channel transmission lines 1, 2, . . . to n having the same number as that of the buffers, whereby respectively transmitting data of color, luminance, subtitle, menu and cursor therebetween. The processing unit 12 performs blending, coding, encoding, scaling and/or de-interlacing of the data stored in the buffers 111, 112, . . . to 11n. FIG. 2 shows a schematic diagram of the operation of a buffer, e.g. buffer 111, in the accessing unit 11, wherein “a” indicates the amount of data temporarily stored in the buffer 111. FIG. 2a shows a schematic diagram of the variation of the amount of data “a”, temporarily stored in the buffer 111, in accordance with time, wherein the buffer 111 sends out data (decreasing part of the curve) after receiving data from the share-bus system 90 (increasing part of the curve).
When the share-bus system 90 is utilized as an input of the multimedia data processing apparatus 10, the accessing unit 11 may alleviate burst-type transfer characteristics on the bus. The buffers 111, 112, . . . to 11n in the accessing unit 11 will sequentially send data request packages, as shown in FIG. 2b, to the share-bus system 90 so as to access data therefrom. When the output of the multimedia data processing apparatus 10 is coupled to a real-time device 20, preferably being a sinker such as television, the processing unit 12 combines the data accessed from the buffers 111, 112, . . . to 11n to a real-time image and sends the image to the real-time device 20. In order to have the real-time device 20 extract complete data, the amount of data “a” stored in the buffers 111, 112, . . . to 11n in the accessing unit 11 must maintain a non-empty status during data transmitting. Therefore, each buffer has to extract enough data from the share-bus system 90 each time, i.e. the length of the data in the data request package as shown in FIG. 2b has to be increased, so as to maintain the non-empty status all the time. However, the size of the buffers 111, 112, . . . to 11n will be increased accordingly such that more data can be temporarily stored in the buffers 111, 112, . . . to 11n.
In contrast, when the input of the multimedia data processing apparatus 10 is coupled to the real-time device 20 (source), such as a video camera, and its output is coupled to the share-bus system 90, the amount of data “a” stored in the buffers 111, 112, . . . to 11n of the accessing unit 11 must maintain a non-full status during data transmitting operation such that the real-time device 20 can continuously transmit data. Therefore, the buffers 111, 112, . . . to 11n must have a larger buffer size so as to maintain the non-full status during data transmitting. This will substantially increase the maximum bandwidth requirement, as shown in FIG. 3.
Referring to FIG. 4, when a plurality of the multimedia data processing apparatuses 10 and the real-time devices 20 are concurrently connected to a shared bus 30, an arbiter 40 may arbitrate among the multimedia data processing apparatuses 10 sequentially to access the data stored in a memory 50, e.g. a double data rate memory. In this structure, waiting time of each multimedia data processing apparatus 10 to access data from the memory 50 becomes longer; therefore, in order to have the data “a” stored in the buffers 111, 112, . . . to 11n maintain in the status of non-empty or non-full, the buffers in the accessing unit 11 of the multimedia data processing apparatus 10 must have a larger buffer size so as to meet the bandwidth requirement for the system.
In lights of the above reasons, because the performance of a system depends on the capability to satisfy the entire bandwidth requirement as all modules are turned on, the above mentioned structure of the multimedia data processing apparatuses 10 may decrease the system performance. Therefore, there exists a need for improving the structure of the multimedia data processing apparatuses so as to decrease the buffer size and bandwidth requirement thereby increasing system performance.